1. Field of the Invention
The present invention relates to an image forming apparatus capable of designating functions of stapling and punching with respect to a sheet.
2. Description of the Related Art
As a sheet processing apparatus for performing post-processing with respect to a sheet delivered from an image forming apparatus, there is a sheet processing apparatus including a punch unit for performing punch processing, and a staple unit for performing staple processing (e.g., see U.S. Pat. No. 5,746,162). In the sheet processing apparatus, it is possible to perform both the punch processing and the staple processing with respect to a sheet.
In the punch processing, it is possible to designate the number, a size, a position, and the like of punch-holes, from an operation part of the image forming apparatus, and to mount on the sheet processing apparatus the punch unit corresponding to a designated content.
In the staple processing, it is possible to designate the staple position (binding position) with respect to one end of a sheet and the number of staple positions. For example, it is possible to designate to staple sheets along one end thereof at one position near a front edge, at one position near a back edge, or at two positions.
However, when the punch processing and the staple processing are performed at the same time, there is a possibility that designation is performed such that the punch processing and the staple processing interfere with each other. When such the designation is performed, a failure may occur in a product. Therefore, in order to prevent the failure from occurring, in the above-mentioned sheet processing apparatus, it is determined whether or not the designated punch position and staple position interfere with each other, and when the positions thereof interfere with each other, control for inhibiting a staple operation performed by the staple unit is performed.
The staple unit has a structure in which the staple processing is performed with respect to a portion which is a trailing end of a sheet with respect to a transport direction of the sheet.
As the punch unit, there are a small-number-hole punch unit for punching a small number of holes, for example, two to four holes, a thirty-hole punch unit for punching a thirty of holes, for example, twenty-six or thirty holes, and the like. The small-number-hole punch unit performs the punch processing with respect to a trailing end of a sheet (i.e., a portion which is the trailing end of the sheet with respect to the transport direction of the sheet). On the other hand, the thirty-hole punch unit often has a structure for performing the punch processing with respect to a leading end of the sheet (i.e., a portion which is the leading end of the sheet with respect to the transport direction of the sheet).
When the punch processing is applied to the trailing end of the sheet, it is necessary to switch back a sheet to be transported and abut the trailing end of the sheet against an abutting member so as to enhance accuracy of the punch processing. Then, the punch processing is performed with respect to the sheet of which trailing end is abutted against the abutting member. In this case, there is a disadvantage that productivity is lowered by switching back the sheet.
On the other hand, when the punch processing is applied to the leading end of the sheet, the abutting member is used in a similar manner as in the punch processing applied to the trailing end of the sheet. However, it is unnecessary to switch back the sheet, so there is an advantage in productivity compared with the case where the punch process is applied to the trailing end of the sheet. As a result, the thirty-hole punch unit often has a structure in which the punch processing is applied to the leading end of the sheet from the viewpoint of the accuracy and productivity of the sheet, as described above.
For example, a case where thirty-hole punch processing and staple processing are sequentially performed by using the thirty-hole punch unit for performing the punch processing with respect to the leading end of the sheet will be described with reference to FIG. 18.
FIG. 18 is a diagram showing an example of a product obtained in the case where the thirty-hole punch processing and the staple processing are performed with respect to the leading end of the sheet by using the thirty-hole punch unit in a conventional sheet processing apparatus.
In this case, a punch position is set to a leading end side of the sheet, and the staple position is set to a trailing end side of the sheet. Thus, in the conventional control described above, the punch position and the staple position do not interfere with each other, so the staple operation performed by the staple unit is not inhibited, and both the thirty-hole punch processing and the staple processing are executed. As a result, as shown in FIG. 18, the product in which the punch processing and the staple processing are applied to different ends of a sheet is outputted. However, such the product is not desirable for a user.